Two projects were carried out to assess possible adverse effects associated with low level exposure to mercury. In the first study, the effect on offspring of dental work during pregnancy was explored in a cohort study that had been carried out in Bristol including all children born to mothors in Bristol and surrounding areas between April 1991 and December 1992. Under the British medical system, expectant mothers are provided enhanced dental services during pregnancy which potentially exposes the fetus to increased levels of mercury. The study aslo explored the consumption of fish which can be a source of exposure to neurotoxins such as mercury. The neurotoxic potential of mercury was explored by assessing the neurodevelopment of offspring using standardized tests administered at 15 and 18 months of age. The aim of the second project was to evaluate the hypothesis that chronic low-level mercury exposure from dental amalgam increases diastolic blood pressure and risk of hypertension. Data from the First National Health and Nutrition Survey (NHANES I) were used. Exposure to dental amalgam fillings was estimated from the number of filled posterior tooth surfaces. Analysis was restricted to whites, age 25 or over and performed separately by gender and age group. Results from the study in the UK showed no adverse consequences for offspring associated with dental treatment of the mother during pregnancy. Maternal fish consumption was found to be beneficial rather than detrimental to the neurodevelopment of the child. See project Z01-ES-49021 for further details. Preliminary results of the analysis linking number of fillings reported in the NHANES study with blood pressure levels and diagnosed hypertension showed no overall association. On the other hand, among women age 40-60 years there was a positive relationship between number of filled posterior surfaces and diastolic blood pressure after adjustment for covariates. An exposure of 21 filled amalgam surfaces corresponded to an average increase in blood pressure of 2.5 mm Hg. A 1.7 fold increased risk of hypertension was found for young men (age 25-40) at 21 filled surfaces. Because there was considerable measurement error in our exposure measure, and because millions of people worldwide are exposed to mercury vapor from dental amalgam, we suggest that additional studies are needed to evaluate whether low-level chronic exposure to mercury, like lead and arsenic, might increase blood pressure and risk of hypertension.